The present disclosure relates to a communication device and a wireless communication device.
A wireless local area network (LAN) system includes wireless LAN access points (hereinafter, also simply referred to as “access points”) and wireless LAN devices (hereinafter, also referred to as “clients”) which can be connected by radio to the wireless LAN access points. In networks such as wireless LANs, access points provide a connection service for clients. Roaming is performed as described below with use of wireless LAN access points and a wireless LAN device (here, roaming means that the wireless LAN device continues communication while moving by disconnecting from one wireless LAN access point and connecting to another wireless LAN access point).
First, the wireless LAN device connects to a wireless LAN access point. Then, the wireless LAN device performs communication via the wireless LAN access point. When the state (for example, the reception sensitivity or the packet rate) of the communication being performed with the connected wireless LAN access point satisfies a roaming start condition, the wireless LAN device detects a roaming-destination wireless LAN access point. Then, the wireless LAN device again connects this time to the roaming-destination wireless LAN access point. Since clients and access points are designed without considering roaming, a long period of time is required for roaming. Therefore, packet loss or packet delay tends to occur during roaming. As a result, such packet loss or packet delay which may occur during roaming causes an instantaneous interruption in sound, frame skipping in moving image, and the like in communications for sounds and moving images, which should be performed in real time. Possible reasons for this problem are described below. In roaming, a client has to disconnect from the currently-connected access point and connect to a roaming-destination access point. Some clients have a strict roaming start condition (in order to maintain the connection to the currently-connected access point for a long period of time), causing packet loss or packet delay when the reception sensitivity or the communication speed is reduced. Further, it takes a period of time to detect a roaming-destination access point.
In the above case, the roaming start condition can be eased. However, when the roaming start condition is eased, a client needs to successively repeat disconnection and connection processing with a plurality of access points, depending on the positional relationship between the client and the access points. When such connection processing is repeated, a radio band may be occupied. In order to solve the problem, a wireless LAN switch allowing high-speed roaming can be used, but it costs as much as tens of thousands of dollars for installation.
[Patent document 1] Japanese Patent Application Laid-Open Publication No. 2002-26931
[Patent document 2] Japanese Patent Application Laid-Open Publication No. 2003-78535
[Patent document 3] Japanese Patent Application Laid-Open Publication No. 2004-180123